The present invention relates to an electric motor, in particular a wiper motor, for wiping a rear window of a motor vehicle.
Numerous electric motors as wiper motors are already known. In the case of these electric motors, the armature shaft of the electric motor has, at one end, a gearing having a worm gear that drives a large worm gear. Situated at this worm gear is a conversion gearing that converts the rotating motion of the gear wheel into a pendulum motion of a wiper shaft. A transmitter magnet is situated on the side of the worm gear opposite the conversion gearing. A Hall-effect sensor connected to an electronics reads off the position, in particular the park position, of the wiper motor. The arrangement on the side opposite the conversion gearing is necessary since the transmitter magnet must move away at a very close distance under the Hall-effect sensor in order to ensure reliable park position detection.
In this context, it is problematic that in the manufacturing sequence, the motor must be turned over once since the conversion gearing and gear cover must be assembled on one side, and the plastic housing, including the printed circuit board and Hall-effect sensor, must be assembled from the opposite back side.
The electric motor according to the present invention has the advantage that as a result of the one-sided arrangement of the gear elements, the sensor device, the signal transmitter, and the printed circuit board, the turning of the electric motor during the manufacturing sequence is eliminated without reducing the reliability of the park position detection, thereby resulting in significant simplification and savings. Thus, the gear housing can be fitted on one side with the worm wheel, the conversion gearing, and the sensor device.
It is particularly advantageous when the sensor device has at least one Hall-effect sensor and the signal transmitter at least one transmitter magnet. Hall-effect sensors and transmitter magnets are available as inexpensive production goods of uniform quality.
A further advantage results when the signal transmitter and the conversion gearing are situated on the same side of the worm gear, thereby ensuring quick assembly and the best possible accessibility in the case of repairs.
The electrical leads of the sensor device being formed in such a manner that the distance between the signal transmitter and the sensor device is minimal results in a further advantage since the sensor device can reliably detect as a result of the minimal distance and no further holding devices are needed for the sensor device due to the forming of the leads.
In particular, it is advantageous to form a flexible printed circuit board in such a manner that the distance between the signal transmitter and the sensor device is minimal. In this manner, optimum signal quality is ensured, a flexible printed circuit board allowing in turn that no further holding elements are needed for the sensor device.
If the sensor device is supported by a plastic part produced using spatial injection-molding, circuit-carrier technology (MID), no further holding elements are necessary for the sensor device, especially when the plastic part is also used as a cover.
If the gearing further has a neutral position in which the distance between the conversion gearing and the signal transmitter is at a maximum, the magnetic flux of the transmitter magnet is not short-circuited by the magnetic material of the conversion gearing, thereby also preventing remanence occurrences in the conversion gearing.
In particular, it is advantageous when, in a park position corresponding to the neutral position, the distance between the signal transmitter and the sensor device is at a minimum. This is then the case when the transmitter magnet comes to rest under the Hall-effect sensor, so that it emits a switching signal (LOW-level) when the park position is reached.
Furthermore, it is advantageous to manufacture the conversion gearing from a non-magnetic material since remanence occurrences can be completely ruled out in this manner. In particular, the transmitter magnet in the neutral position can, therefore, also be situated in the region of the conversion gearing in this case.